Influence of Various Additives on Properties of α-Tricalcium Phosphate-Polycarboxylic Acid Complexes

Abstract

When α-tricalcium phophate (α-TCP) powder is mixed with a polycarboxylic acid solution, an α-TCP-polycarboxylic acid complex is formed and hardens. The purpose of this study was to investigate the influence of various additives on the physical properties of α-TCP-polycarboxylic acid complexes as a basic study of new calcium phosphate materials incorporating α-TCP. Ground α-TCP powders were mixed with various additives. ZnO, MgO, ZrO₂, TiO₂ and α-Al₂O₃ were used as the additives. The mixing liquid for dental polycarboxylate cement (HY-BOND polycarboxylate cement, Shofu) was polycarboxylic acid solution. After the α-TCP powders, each containing a different additive, were mixed with the polycarboxylic acid solution at a powder/liquid ratio=1.2/1.0 (g/g), the setting time, compressive strength, and solubility and disintegration of the complexes were measured by the methods specified by ADAS No.61 for zinc polycraboxylate cement. Also, the complexes were analyzed by X-ray powder diffraction analysis and observed with a scanning electron microscope. The addition of the individual oxides to the complexes generally increased the setting time, especially in the case of ZnO. Although the presence of a small amount of additive in the complexes slightly increased the compressive strength, it was impossible to increase significantly the strength by the addition of the oxides used in this study. The addition of ZrO₂ or TiO₂ decreased the solubilty and disintegration of the complex;however, that of ZnO or MgO increased the solubility and disintegration. X-ray diffraction analysis of the complexes showed amorphous patterns and the unreactive α-TCP and/or additives were identified. Scanning electron microscopic observation indicated that the complexes consisted of a matrix and unreactive α-TCP and/or additive particles. The results suggest that the presence of additives that react rapidly with the polycarboxylic acid solution remarkably affected the setting reaction and physical properties of the complexes.